Session D10: Inflation, Dark Energy, and Baryogenesis

Scalar perturbations in massive gravity in the presence of matter

The de Rham-Gabadadze-Tolley (dRGT) theory provides a consistent massive extension of general relativity, but stable self-accelerating solutions within it have been elusive. The quasi-dilaton extension of the dRGT theory allows for such solutions by introducing an additional scalar field with a global rescaling symmetry. In this talk, I will discuss scalar perturbations in the extended quasi-dilaton theory in the presence of matter. I will first briefly introduce the theory and the self-accelerating background evolution where the quasi-dilaton (in the presence of a massive graviton) can act as an effective cosmological constant. I will next discuss the general calculation of scalar perturbations without restricting to any choice of gauge. I will then choose a particular form for matter where a unitary gauge for matter fields is most convenient to work in and present the kinetic matrix calculation for all propagating scalar degrees of freedom. I will show that the conditions for positive eigenvalues can be satisfied, and the theory can thus remain ghost-free on the self-accelerating solution in the presence of matter. Lastly, I will briefly discuss the linear growth of structure in this theory, that the next talk will describe in more detail.   

Cosmological constraints on massive gravity

As discussed in the previous talk, a promising approach to explain the current accelerated expansion of the Universe is to extend general relativity to include a non-zero graviton mass. The resulting modification is expected to lead to different background expansion and growth of structure compared to the standard cosmological constant with cold dark matter model. In this talk, I will present results on the growth of matter perturbations in a quasidilaton extension of the de Rham-Gabadadze-Tolley (dRGT) theory of massive gravity, that allows for a stable cosmology. Starting in conformal Newtonian gauge, where scalar perturbations coincide with gauge-invariant ones, I will first obtain coupled differential equations in all propagating degrees of freedom. I will next discuss two sub-horizon approximations that allow us to find a single equation describing the growth of matter perturbations and show how the resulting growth of structure compares to the standard cosmological model. Lastly, I will discuss the constraints on various model parameters, including the mass of the graviton, from a Markov-Chain Monte-Carlo analysis that compares the background evolution to supernovae data and the growth of perturbations to galaxy clustering data.   

BICEP/Keck Constraints on Attractor Models of Inflation and Reheating

Recent BICEP/Keck data on the cosmic microwave background, in combination with previous WMAP and Planck data, impose strong new constraints on the tilt in the scalar perturbation spectrum, n_s, as well as the tensor-to-scalar ratio, r. These constrain the number of e-folds of inflation, N*, the magnitude of the inflaton coupling to matter, y, and the reheating temperature, T_RH. We evaluate the number of e-folds N* numerically in attractor models of inflation (T-Models and E- Models). We show that the 68% C.L. region of (n_s, r) plane favors large values of N*, y, and T_RH, and these parameters are constrained by the production of gravitinos and supersymmetric dark matter. We also show the minimum reheating temperature that is compatible with Big Bang Nucleosynthesis (BBN). Finally, we discuss the impacts of the BICEP/Keck and other constraints on E- and T-Models of inflation.   

Searching for Chameleon Dark Energy with Mechanical Systems

We consider using optically levitated microspheres and torsion balances as screened scalar field detectors. We present a novel derivation for the classical chameleon force between two spherical bodies which remains valid at smaller separation distances and stronger chameleon couplings than previous work. Using this and experimental sensitivities achieved by the current generation of experiments, we show predicted constraints on chameleons as dark energy. We include analytic expressions for the parameter space that can be probed by future experiments in terms of experimental parameters. We also indicate regions of theoretically well-motivated chameleon parameter space which should be the aim for future experiments.   

Signature of heavy physics in stochastic gravitational-wave background

Sudden onset of classical oscillations of a heavy field (mass greater than the inflationary Hubble scale) leaves a characteristic scale-invariance-breaking oscillatory feature in the power spectrum of primordial fluctuations. The presence of these features provides a unique opportunity to detect the dynamics of heavy fields during inflation. While such features are constrained to be small in curvature perturbations, we show that it may not be the case for isocurvature perturbations. I will demonstrate the possibility of observing large primordial features in the stochastic gravitational-wave (GW) background originating from a first-order phase transition in a hidden sector. I will show that the signal can be observably large in the GW map while being completely hidden in the standard curvature perturbations such as those of the Cosmic Microwave Background.   

Dark energy of the photon space, inflation of the charged black holes and universe evolution

Space-time evolution of our universe is explained by using the 3-dimensional quantized space model (TQSM) based on the 4-dimensional (4-D) Euclidean space. The energy (E = cΔtΔV), charges and energy density (|q| = ρ = cΔt) and absolute time (ct) are newly defined based on the 4-D Euclidean space. The photon flat space with the constant energy density of ρ = cΔt_q is proposed as the dark energy (DE). The dark energy is separated into the ν DE and photon DE which create the new photon spaces with the constant energy density of ρ = cΔt_q. The v DE is from the ν pair production by the CPT symmetry and the photon DE is from the photon space pair production by the T symmetry. The vacuum energy crisis and Hubble’s constant puzzle are explained by the photon space with the ν DE and photon DE. The big bang and inflation of the primary black hole is connected to the accelerated space expansion and big collapse of the photon space through the universe evolution. The big bang from the nothing is the pair production of the matter universe with the positive energy and the partner anti-matter universe with the negative energy from the CPT symmetry. Our universe is the matter universe with the negative charges of electric charge (EC), lepton charge (LC) and color charge (CC).    

Testing Affleck-Dine Baryogenesis with Gravitational Waves

The source of the observed cosmological baryon excess is unknown, but a popular proposal is Affleck-Dine baryogenesis.  In this model, the asymmetry is produced during the evolution of a scalar condensate, which fragments into non-topological solitons (Q-balls).  If these Q-balls are sufficiently long-lived, then they may dominate the energy density of the universe before decaying, releasing their baryon charge into the plasma.  The decays of charged quanta into Standard Model fermions can occur only at the surface of the Q-ball, and so the decay rate increases as the Q-ball shrinks.  From a cosmological perspective, Q-ball decay is effectively instantaneous, similar to black hole decay, and so the universe undergoes a rapid transition from matter to radiation domination.  The Q-ball overdensities become sound waves in the plasma, which source gravitational waves, and a particular frequency is resonantly enhanced (as with primordial black holes, the so-called "poltergeist mechanism").  For well-motivated regions of parameter space, this peak is in the detectable range of the Einstein telescope and/or DECIGO, providing a new opportunity to test Affleck-Dine baryogenesis.   

Decaying Dark Matter at IceCube and its Signature in High-Energy Gamma-Ray Experiments

Observations of high-energy astrophysical neutrinos in IceCube have opened the door to multi-messenger astronomy, by way of which questions in particle physics could be explored through a combination of IceCube data and optical experiments such as Fermi-LAT. However, the origin of these astrophysical neutrinos is still largely unknown. Among the tensions that still need to be addressed, for example, is the excess of neutrinos observed in the energy range of 40-200 TeV, a contribution that could come from heavy dark matter decay. The dark matter decay hypothesis can be tested through comparisons with gamma-ray data, because a coincident gamma-ray flux is expected to accompany the neutrino flux that IceCube observes. However, gamma-rays become heavily suppressed for sources dominating in particular energy ranges. In the case of the Galactic center, the $\gamma$-sky is partially opaque in the (0.1-10) PeV range. This is due to properties of the traversed medium, which consists of extragalactic background light (EBL), the cosmic microwave background (CMB), and the intergalactic magnetic field. These significantly alter the initial spectrum through intermediate processes such as absorption and Inverse-Compton scattering, giving rise to anisotropy and energy features in the final spectrum that reaches telescopes on Earth. The existence of competing photon background models, moreover, complicates estimates of dark matter constraints. In this presentation, we address these questions by studying the impact that these different models have on indirect measurements of heavy dark matter decay. I present my predictions for galactic, inverse-Compton, and extragalactic gamma-ray spectra undergoing attenuation by different backgrounds.   

Lambda as a Measure of the Rate of Recursion of Geometric Algebras

Geometric algebras over the real numbers are isomorphic to certain matrices–dyreal, real, complex, quaternionic, or dyquaternionic–depending only on the metric signature s, the number of spatial dimensions minus the number of temporal dimensions. The rank of each kind of matrix depends only on the total number n of dimensions, spatial plus temporal. Geometric algebras over the reals are periodic in s, but recursive in n. The recursion is generated from the anticommuting basis vectors of either the Euclidean plane or the Minkowskian plane. Certain direct products of the geometric elements of these two planes form the basis vectors of 4-dimensional Minkowskian space-time if the resulting basis vectors do not curl up on themselves. If they do, the resulting geometric algebra generates the Standard Model of physics, with 4 real dimensions of space-time and 12 real curled-up dimensions (rather than the 6 complex curled-up dimensions of M-Theory). After eight dimensions, the pattern of geometric algebras repeats itself, resulting in a recursively generated, exponentially expanding space-time lattice with the Standard Model at each node of the lattice. The cosmological constant is set by the rate of recursion, a different process from the curling-up process that sets the Planck scale.